*NSYNC Exploring Arena Tour Possibilities Amid 30th Anniversary

Four of the five members of *NSYNC are in serious talks about giving fans the reunion they’ve been waiting for -- even if Justin Timberlake doesn't sign on ... TMZ has learned.

Sources familiar with the situation tell TMZ ... Lance Bass, Joey Fatone, JC Chasez, and Chris Kirkpatrick have been discussing big plans for the group's 30th anniversary, including the possibility of an arena tour without JT. We're told the guys know demand is still sky high, and promoters believe fans will pack arenas even with just 4 of them.

As we first reported, the foursome were eager to sign onto a massive stadium tour deal from Live Nation and AEG last August for a 2026 run. The offer was presented to all five, but Justin never engaged -- long before his Lyme disease diagnosis made headlines.

Now, promoters have drawn up proposals for a 4-piece arena tour, convinced the group could sell out multiple shows in major cities. Of course, if JT joined, demand could skyrocket to stadium-level runs with multiple dates.

While talks are ongoing among the 4, the guys are hopeful Justin will eventually come around for a full-fledged stadium tour.

Fans will remember ... reunion buzz has been building -- from the 2023 MTV VMAs, to recording a "Trolls" track, walking the premiere carpet together, and surprising JT's L.A. tour crowd onstage. The four also got a taste of the frenzy at Coachella 2019 without Timberlake.

And adding fuel to the fire ... their smash hit "Bye Bye Bye" became a global hit all over again in 2024 after being featured in the "Deadpool" movie.